The use of ceramics in the fabrication of structural components possessing good mechanical properties at high temperatures has in recent years been the subject of intensive research. Because it exhibits high strength at elevated temperatures and excellent thermal shock, creep and oxidation resistance, silicon nitride has been of particular interest.
The usual procedure in fabricating structural components from silicon nitride is to reaction sinter, hot press or pressure reaction sinter particulate silicon nitride in admixture with a sintering aid, such as magnesium oxide or alumina. To obtain a structural component having optimum physical properties, it is necessary that the silicon nitride be of very high purity and in finely divided form. Also, alpha phase silicon nitride powder or a precursor therefor should be used as the starting material because higher strength and more uniform structures are obtained by hot pressing than when beta phase silicon nitride is present in any appreciable amount in the starting material. Still further, the sintering aid used must be in finely divided form, of high purity and of a nature such that it will not have an adverse effect upon the physical properties of the compressed article. In other words the sintering aid must not be such that it will function as an impurity in degrading physical properties.
It is an object of this invention to provide an improved method for fabricating articles from silicon nitride.
Another object of the invention is to provide new and improved sintering aids for use with silicon nitride in fabricating articles by hot pressing.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.